In the blowhead mechanism of the Hartford I.S. machine, the blowhead support arm is clamped to a vertical, reciprocable piston rod whose lower end carries a cam which rides in a cam slot and whose upper end telescope into an annular support member. Typically, when it is desired to have the blowhead mechanism placed in its "parked" position, it was accomplished by the air operated piston rod being held in position by application of air to the underside of the driving piston. The prior art teaches the use of a safety lock being accomplished by the introduction of safety air into the system through a valve being set. An example of such art is U.S. Pat. No. 2,542,086 issued Feb. 20, 1951.
Another prior art patent, U.S. Pat. No. 1,911,119 issued May 23, 1933, shows in FIG. 4, a pneumatic mechanism for operating a "settle-blow" head 85, funnel 55 as well as a parison blowing head 257. The similarity of these mechanisms is such that they operate in similar manners. Each of these mechanisms have a "parked" position which is at a level above its operational level.